John L. Ulmer

Blind source separation of multiple signal sources of fMRI data sets using independent component analysis.

PURPOSE The objective of this study was to separate multiple signal components present in functional MRI (fMRI) data sets. Blind source separation techniques were applied to the analysis of fMRI data to determine multiple physiologically relevant independent signal sources. METHOD Computer simulations were performed to test the reliability and robustness of the independent component analysis (ICA). Four subjects (3 males and 1 female between 14 and 29 years old) were scanned under various stimulus conditions: (1) rest while breathing room air, (2) bilateral finger tapping while breathing room air, and (3) hypercapnia during bilateral finger tapping. RESULTS Simulations performed on synthetic data sets demonstrated that not only could the algorithm reliably detect the shapes of each of the source signals, but it also preserved their relative amplitudes. The algorithm also performed robustly in the presence of noise. With use of fMRI time series data sets from bilateral finger tapping during hypercapnia, distinct physiologically relevant independent sources were reliably estimated. One independent component corresponded to the hypercapnic cerebrovascular response, and another independent component corresponded to cortical activation from bilateral finger tapping. In three of the four subjects, the underlying fluctuations in signal related to baseline respiratory rate were identified in the third independent component. Principal component analysis (PCA) could not separate these two independent physiological components. CONCLUSION With use of ICA, signals originating from independent sources could be separated from a linear mixture of observed data. Limitations of PCA were also demonstrated.

Lesion-induced pseudo-dominance at functional magnetic resonance imaging: implications for preoperative assessments

OBJECTIVE:To illustrate how lesion-induced neurovascular uncoupling at functional magnetic resonance imaging (fMRI) can mimic hemispheric dominance opposite the side of a lesion preoperatively. METHODS:We retrospectively reviewed preoperative fMRI mapping data from 50 patients with focal brain abnormalities to establish patterns of hemispheric dominance of language, speech, visual, or motor system functions. Abnormalities included gliomas (31 patients), arteriovenous malformations (AVMs) (11 patients), other congenital lesions (4 patients), encephalomalacia (3 patients), and tumefactive encephalitis (1 patient). A laterality ratio of fMRI hemispheric dominance was compared with actual hemispheric dominance as verified by electrocortical stimulation, Wada testing, postoperative and posttreatment deficits, and/or lesion-induced deficits. fMRI activation maps were generated with cross-correlation (P < 0.001) or t test (P < 0.001) analysis. RESULTS:In 50 patients, a total of 85 functional areas were within 5 mm of the edge of a potentially resectable lesion. In 23 of these areas (27%), reduced fMRI signal in perilesional eloquent cortex in conjunction with preserved or increased signal in homologous contralateral brain areas revealed functional dominance opposite the side of the lesion. This suggested possible lesion-induced transhemispheric cortical reorganization to homologous brain regions (homotopic reorganization). In seven patients, however, the fMRI data were inconsistent with other methods of functional localization. In two patients with left inferior frontal gyrus gliomas and in one patient with focal tumefactive meningoencephalitis, fMRI incorrectly suggested strong right hemispheric speech dominance. In two patients with lateral precentral gyrus region gliomas and one patient with a left central sulcus AVM, the fMRI pattern incorrectly suggested primary corticobulbar motor dominance contralateral to the side of the lesion. In a patient with a right superior frontal gyrus AVM, fMRI revealed pronounced left dominant supplementary motor area activity in response to a bilateral complex motor task, but right superior frontal gyrus perilesional hemorrhage and edema subsequently caused left upper-extremity plegia. Pathophysiological factors that might have caused neurovascular uncoupling and facilitated pseudo-dominance at fMRI in these patients included direct tumor infiltration, neovascularity, cerebrovascular inflammation, and AVM-induced hemodynamic effects. Sixteen patients had proven (1 patient), probable (2 patients), or possible (13 patients) but unproven lesion-induced homotopic cortical reorganization. CONCLUSION:Lesion-induced neurovascular uncoupling causing reduced fMRI signal in perilesional eloquent cortex, in conjunction with normal or increased activity in homologous brain regions, may simulate hemispheric dominance and lesion-induced homotopic cortical reorganization.

Diffusion Tensor MR Imaging in Chronic Spinal Cord Injury

BACKGROUND AND PURPOSE: Diffusion tensor MR imaging is emerging as an important tool for displaying anatomic changes in the brain after injury or disease but has been less widely applied to disorders of the spinal cord. The aim of this study was to characterize the diffusion properties of the entire human spinal cord in vivo during the chronic stages of spinal cord injury (SCI). These data provide insight into the structural changes that occur as a result of long-term recovery from spinal trauma. MATERIALS AND METHODS: Thirteen neurologically intact subjects and 10 subjects with chronic SCI (>4 years postinjury) were enrolled in this study. A single-shot twice-refocused spin-echo diffusion-weighted echo-planar imaging pulse sequence was used to obtain axial images throughout the entire spinal cord (C1-L1) in <60 minutes. RESULTS: Despite heterogeneity in SCI lesion severity and location, diffusion characteristics of the chronic lesion were significantly elevated compared with those of uninjured controls. Fractional anisotropy was significantly lower at the chronic lesion and appeared dependent on the completeness of the injury. Conversely, mean diffusivity measurements in the upper cervical spinal cord in subjects with SCI were significantly lower than those in controls. These trends suggest that the entire neuraxis may be affected by long-term recovery from spinal trauma. CONCLUSION: These results suggest that diffusion tensor imaging may be useful in the assessment of SCI recovery.

Klippel-feil syndrome: Ct and mr of acquired and congenital abnormalities of cervical spine and cord

We reviewed MR and CT myelographic studies in patients with the Klippel-Feil syndrome (KFS) to determine the patterns of associated congenital and acquired abnormalities of the spine and spinal cord and to correlate these radiologic findings with the manner of clinical presentation. Twenty-four consecutive patients with radiologically definite KFS were evaluated by a cross-sectional imaging technique (CT or MR) over a 6 year period. Radiologic images were blindly interpreted by a panel of three experienced neuroradiologists and then correlated with clinical history. Cervical spondylosis or disk herniations were the most common radiologic abnormalities encountered, seen in 10 (42%) of the 24 patients. While some clustering of these secondary degenerative changes occurred at levels immediately adjacent to the fused vertebrae, in most patients spondylotic changes were seen widely distributed throughout the lower cervical region. Coexisting congenital defects of the spinal cord or brain were encountered in seven patients, six of whom were female, consisting of cervical cord dysraphism or diastematomyelia (n = 5) and Chiari I malformations (n = 2). In only eight patients (33%) had the diagnosis of KFS been suspected clinically prior to imaging by the presence of short neck, limited cervical mobility, or low occipital hairline. In the remaining 16 patients, mostly adolescents or adults being evaluated for cervical sensory or motor syndromes, the diagnosis of KFS was made radiologically at the time of the imaging referral.

Association, commissural, and projection pathways and their functional deficit reported in literature.

Abstract: This study demonstrates normal white matter structures of the supratentorial system revealed by diffusion tensor imaging. Their anatomic connections and functional significance are discussed in the context of the lesion-induced deficits reported in the literature, which may not fully represent the lesion-induced effects on the white matter function and may not be entirely specific to the tract discussed. Nevertheless, understanding the most common effects of lesions on the functional connectivity provides a framework that we can use in advanced neuroimaging studies, like diffusion tensor imaging, functional magnetic resonance imaging, and positron emission tomography, and in our daily clinical practice.

The Role of Diffusion Tensor Imaging in Establishing the Proximity of Tumor Borders to Functional Brain Systems: Implications for Preoperative Risk Assessments and Postoperative Outcomes:

Diffusion Tensor Imaging (DTI) is a new MRI imaging technique sensitive to directional movements of water molecules, induced by tissue barriers. This provides a new form of contrast that allows the identification of functional white matter tracts within the brain, and has been proposed as a technique suitable for presurgical planning in brain tumor patients. Resection of primary brain tumors improves survival, functional performance, and the effectiveness of adjuvant therapies, provided that surgically-induced neurological deficits can be avoided. Diffusion Tensor Imaging (DTI) has the potential to establish spatial relationships between eloquent white matter and tumor borders, provide information essential to preoperative planning, and improve the accuracy of surgical risk assessments preoperatively. We present our experience in a series of 28 brain tumor patients where the integration of functional magnetic resonance imaging (fMRI) and DTI data was used to determine key anatomic spatial relationships preoperatively. Twice as many functional systems were localized to within 5 mm of tumor borders when DTI and fMRI were utilized for preoperative planning, compared to that afforded by fMRI alone. Our results show that the combined use of fMRI and DTI can provide a better estimation of the proximity of tumor borders to eloquent brain systems sub-serving language, speech, vision, motor and premotor functions. Additionally, a low regional complication rate (4%) observed in our series suggests that preoperative planning with these combined techniques may improve surgical outcomes compared to that previously reported in the literature. Larger studies specifically designed to establish the accuracy and predictive value of DTI in brain tumor patients are warranted to substantiate our preliminary observations.

Image-guided catheter drainage of the infected pleural space.

Thoracic empyema occurs at all ages and has reported mortality rates of 10% to 75%. Most authors agree that complete drainage of complicated effusions or organized empyemas and reexpansion of atelectatic lung are important in obtaining a satisfactory clinical outcome. For initial tube drainage, a 26-F to 36-F chest tube traditionally has been inserted at the bedside. The results of this method of empyema evacuation have varied widely, with an overall cure rate reported to be 47%. Image-guided placement of smaller 8-F to 14-F catheters has been offered as an alternative therapy with an overall reported cure rate of 81% in 104 patients.

Diffusion Tensor MR Imaging of the Neurologically Intact Human Spinal Cord

BACKGROUND AND PURPOSE: The aim of this study was to characterize the diffusion properties of the entire human spinal cord in vivo. These data are essential for comparisons to pathologic conditions as well as for comparisons of different pulse sequence design parameters aimed to reduce scan time and more accurately determine diffusion coefficients. MATERIALS AND METHODS: A total of 13 neurologically intact subjects were enrolled in this study. A single-shot, twice-refocused, spin-echo, diffusion-weighted, echo-planar imaging (EPI) pulse sequence was used to obtain axial images throughout the entire spinal cord (C1–L1) in 45 minutes. RESULTS: Diffusion images indicated slight geometric distortions; however, gray and white matter contrast was observed. All measurements varied across the length of the cord. Whole cord diffusion coefficients averaged 0.5–1.3 × 10−3 mm2/s depending on orientation, mean diffusivity (MD) averaged 0.83 ± 0.06 × 10−3 mm2/s, fractional anisotropy (FA) averaged 0.49 ± 0.05, and volume ratio (VR) averaged 0.73 ± 0.05. CONCLUSION: This study provided normative diffusion values for the entire spinal cord for use in comparisons with pathologic conditions as well as improvements in pulse sequence design.

Lateral Supratentorial Endodermal Cyst: Case Report and Review of Literature

OBJECTIVE AND IMPORTANCE Epithelial cysts of the central nervous system are unusual entities, with the majority reported to occur in the spinal canal. More unusual is the intracranial presentation, which shows a predilection for midline localization in the posterior fossa, brainstem, and suprasellar regions. This report discusses the differential diagnosis, pathogenesis, radiographic presentation, and therapeutic considerations of a laterally positioned cerebral convexity endodermal cyst. CLINICAL PRESENTATION A 49-year-old right-handed man presented with approximately a 30-month history of short- and long-term memory difficulties. A magnetic resonance imaging study revealed a large, nonenhancing, extra-axial cystic lesion overlying the right lateral frontal convexity. INTERVENTION A right frontoparietal craniotomy exposed a large extra-axial cyst with an opaque, yellowish-white membrane containing a mucoid fluid. Histological analysis disclosed a layer of unremarkable, ciliated columnar epithelium with a basement membrane that stained positive for cytokeratin, periodic acid-Schiff, and Alcian blue. No evidence of either a muscular or cartilaginous layer around the mucosa was present to further delineate neurenteric versus bronchogenic origin of the cyst. CONCLUSION This case involved the occurrence of a solitary endodermal cyst as an extra-axial mass localized over the lateral frontal lobe. The lateral supratentorial localization of this lesion illustrates the need for consideration of the pathogenesis of this entity as well as its diagnostic differentiation from other cystic abnormalities in this region. A review of the histochemistry of endodermal, neuroepithelial, and other cerebral cysts is presented.

Congenital cyst of the pancreas.

The case of a 4-month-old girl with a rare multilocular congenital pancreatic cyst is presented, along with radiological/pathological correlation and a review of the literature. Congenital cyst of the pancreas is a rare lesion most often seen in infant girls, although it may be demonstrated in utero. Conventional radiographic signs and clinical symptoms primarily reflect mass effects, whereas imaging modalities show the cystic nature of the mass. Although rare, this cyst should be considered in the differential diagnosis of fetal and pediatric cystic abdominal masses.